Mode transformer



April 17, 1956 s. B. COHN MODE TRANSFORMER Filed Oct. 24, 1950 ATTORNEY2,742,612 MODE TRANSFORMER Seymour B. Cohn, Flushing, N. Y., assignor toSperry Rand Corporation, a corporation of Delaware Application October24, 1950, Serial No. 191,849

' 11 Claims. Cl. 333-21 The present invention relates generally toultrahigh frequency apparatus, and in particular to a mode transformerfor transforming a TE11) mode in a rectangular waveguide to a circularlypolarized TE11 mode in an axially aligned circular waveguide.

In many types of ultra-high frequency equipment it is desirable tocouple a rectangular waveguide to a circular waveguide. In such couplingit is frequently desired that the mode of transmission in therectangular guide be TE and the mode in the circular guide be the TE11mode.

Copending application S. N. 234,l24,filed June 28, 1951, describes sucha structure wherein the axis of the rectangular guide is at right anglesto the circular waveguide.

United States Patent waveguide section 10, is oriented with its axisparallel i dipole 20. As a result, energy is transmitted along co-'axial line section and is radiated into circular waveguide by dipole 25.Because of the orientation of dipole The present invention describes astructure wherein'the same electrical result obtains, but the,rectangular wave guide and the circular guide are in axial alignment.

It is, therefore, an-object of the present invention -to provide a modetransformer for coupling a rectangular two waveguide to a circularwaveguide in which'the guides are in axial alignment.

It is a further object of the present invention to provide a modetransformer for coupling the TE11) mode in a rectangular waveguide to acircularly polarized wave of the TE1 mode in a circular waveguide.

It is still a further object of the present invention to* provide anaxially aligned mode transformer which operates overa relativelybroad'rangeof frequencies.

These and other objects will become more apparent and a betterunderstanding of the invention will result from a consideration of thedrawings in which:

Fig. l is a perspective view partially in section of one embodiment ofthe present invention, i

Fig. 2 is a diagrammatic sketch of the device shown in Fig. l useful inexplaining its operation,

.Fig. 3 is a section view of a modification of th e device shown in Fig.1, and I 7 Figs. 4-6 are perspective views partially ins ection offurther embodiments of the present invention.

Referring now more particularly to Fig. 1, there, is

shown a section of rectangular waveguide 110. having a width a and aheight b.- Rectangular waveguide section 10 abuts end plate 11 ofcircular waveguide section 12,

and is permanently joinedthereto, the two waveguide sections beingaxially aligned.

Acoaxial line section 15 is supported at the junction of rectangularwaveguide section 10 and circular waveguide; section 12,and is orientedalong the common axis 16 of the two waveguide sections. This coaxialsection 15 may be supported in a numberof ways, for example, by a;

dielectric support 17. One end of coaxial line section terminates withinrectangular waveguide section'10 and the other end terminates'withincircular waveguide section 12.

Mounted at each end of coaxial line section is a pickup 1 unit. In Fig.1, these pickup units are shown as dipoles,

although any other similar energy pickup unit may be utilized. Dipole20, which is mounted at that end of coaxial line section 15 whichterminates in rectangular to the shorter dimension of the waveguidecross section.

That is, dipole 20 is so positioned to be excited by the electric vectorof the dominant mode TEm in the rectangular waveguide section 10.

Dipole 25, which is mounted at that end of coaxial line section 15 whichterminates within circular waveguide section 12, is oriented at rightangles to dipole 20. That is, the axis of dipole 2-5 lies along adiameter of circular waveguide section 12 which is parallel to the largedimension' of the 'ci'oss section of rectangular waveguide s'ec-. 'tion10.

I In operation, energy is transmitted along rectangular waveguidesection 10 in the TE10 mode. The electric vector, shown diagrammaticallyas E1 in Fig. 1, excites 25, the radiated energy has its electric vectorat right angles to E1 as is indicated by vector E3.

Since rectangular waveguide section 10 is directly coupled to circularwaveguide section 12 energy will also be coupled directly thereto. Theelectric vector of this directly coupled'energy will, of course, beparallel to the electric vector E1. This is represented by vector E2.

It is immediately seen that the physical orientation of the two electricvectors of the energycoupled from rec tangular waveguide section 10 tocircular waveguide se'c-" tion 12 is one of right angles; that is, theyare physically apart in space.-

By adjusting the length L of the coaxial line section properly, theelectrical orientation of vectors E2 and E3 can be made to be 90 apartin phase. Thus it is seen thatthere are established in the circularwaveguide section 12 two waves of the TE11 mode that are spaced 90 apartelectrically and physically, so that the resultant is a circularlypolarized wave of the TE11 mode. I

Fig. 2 illustrates this effect in somewhat greater detail. The energypassing through the rectangular waveguide section 10 is in the'TE1omode. This energy excites pickup unit 20. In addition, it travels adistance l1 farther inwaveguide section 10. In so doing, shift, 1,-whichis equal to 2 1rl M1 where kgi is the wavelength within guide 10. I

it sulfers a phase The energy'induced in coaxial line section 15 travelsin. Y a TEM mode andsufiers a phase shift, 3, which is equal where K3 isthe dielectric constant .of the coaxial line} section 15 and A is thefreespace Wavelength of the energy.

The energy which is directly coupled into the circular Therefore, allthat is necessary in order to insure E2 and E3 of being in timequadrature is that the following relationship" obtain where n=zero orany integer, and 4:4 is a phase shift approximately independent of l;and Z2 which lumps to- Patented A r. 17,1956;

This energy is in the TE11 mode and suffers gether the individual phaseshifts at the dipoles and at the junction of waveguides and 12.

"Sin'' xgl'and'xg'' vary because of the different guide section andtheir resulting mode differences, it is possible to maintain the overalllength of coaxial line section cfonstant and vary the ratio 11/12 andthus adjust the deviceto operate over a range a frequencies. Such asiructure is shown in Fig. 3. In this figure, coaxial line section 15 issupported on a dielectric slide 30 which passes through a wall ofrectangular waveguide section By adjusting the longitudinal position ofslide 3t), the ratio of Il iIO 12 may be varied. This changes 51, and1155, so that the desired 90 phase shift occurs at a selected operatingfrequency.

As stated above, the invention is not intended to be limited to the useof dipoles as pickup units, but other forms such as loops and probes maybe used with equal facility. The only requirement in the type used isthat the pickup unit inserted in the rectangular guide be excited by theregular TEio mode, and that the pickup unit in the circular guide excitea TEll mode having a plane of polarization which is at right angles tothe electric vector of the TEio mode.

In addition, the invention is in no way limited to coaxial line forcoupling. Instead a two wire transmission line may also be utilized.

It should further be pointed out that, although the operation of thedevice is described as transforming energy from the 'IEm mode in therectangular guide to a circularly polarized wave of the T1511 mode inthe circular guide, the structure will also operate in the reversedirection. In Fig. l, dipole 25 will be excited by the horizontalcomponent of an incident circularly polarized wave, which will enabledipole to excite a T510 mode in rectangular guide 10.

In some cases, it may be necessary to minimize phase shifts due to thediscontinuity of the two wave guide sections. Another embodiment of thepresent invention is shown in Fig. 4. In this embodiment rectangularguide section couples to an intermediate rectangular guide section 40which in turn couples to circular guide section 12. By using such anintermediate guide section 40, the effect of the discontinuities may bereduced. Knob 41 is utilized to adjust the position of coaxial waveguide section 15, longitudinally as before.

In order to further reduce the discontinuities, a taper section could beapplied between rectangular'wave guide section 10 and rectangular waveguide section 40. This embodiment is illustrated in Fig. 5, with tapersection 50 inserted.

Fig. 6 shows a further modification in which a flared section 60 isinserted between rectangular wave guide section 10 and circular waveguide section 12. As before, coaxial line section 15 is inserted thereinand may be longitudinally positioned by knob 61.

It is thus seen that the present invention provides a mode transformerfor coupling a rectangular wave guide to a circular wave guide, the twoguides being in axial alignment. The invention further provides astructure for coupling the T1510 in the rectangular guide to a circularpolarized wave of the T1511 mode in a circular wave guide. Stillfurther, the present invention provides an axially aligned modetransformer which is capable of operating efficiently over a range oroperating frequencies.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An electromagnetic wave energy mode transformer comprising a sectionof rectangular waveguide, a section of circular waveguide, saidwaveguide sections having wave energy propagation axes in substantialalignment, means for coupling wave energy directly between said waveuide sections, a section of"coaxial transmission line extending throughsaidfmeans and having one end portion thereof extending within saidrectangular waveguide section and having the other end portion thereofextending within said circular waveguide section, and wave energypick-ups terminating the ends of said coaxial line section and orientedto couple said coaxial line section to said circular Waveguide sectionwith a fundamental trans verse electric wave energy mode having itselectric field vector in quadrature relative to the electric fieldvector of the wave energy field in said waveguide section, whereby thewave energy phase transitions provided by said coupled waveguidesections, said means, and said coaxial line section cooperate with saidoriented pick-ups to maintain a wave energy mode transformation betweena transverse electric wave energy mode in said rectangular section and acircular-polarizedfundamental transverse electric wave energy mode insaid circular waveguide section.

2. An electromagnetic wave energy mode transformer comprising acontinuous length of hollow wave guide having a central longitudinalaxis of propagation, a first portion of said wave guide beingrectangular in crosssection and a second portion of said wave guidehaving a circular cross-section, a transmission line positioned withinsaid wave guide along said axis of propagation, means for supportingsaid line, and energy pick-up and radiating'means terminating each endof the transmission line, the ends of the transmission line terminatingrespectively in the rectangular and circular portions of the wave guide'.3. An electromagnetic wave energy mode transformer as described inclaim 2 wherein said transmission line is a coaxial line section.

4. An electromagnetic wave energy mode transformer as described 'inclaim 3' wherein said energy pick-up and radiating means is a dipoleelement, the dipoles at each end of the coaxial line section beingoriented at substantially with respect to each other.

5. Apparatus as defined in claim 4 wherein the means for supporting thecoaxial line is adjustable longitudinally of the 'wave guide.

6. Apparatus as defined in claim 2 wherein said wave guide includes aportion of wave guide intermediate said circular and rectangularportions.

7. Apparatus asdefinedin claim 6 wherein said intermediate portion isrectangular and substantially larger in cross-sectional dimensions thanthe first-mentioned rectangular portion but no't'larger in anycross-sectionaldirh'ension than the diameter of said circular portion.

8. Apparatus as dfefined in claim 7 wherein a tapered line section joinssaid'interrnediate portion and said firstmentioned rectangular portionof the wave guide.

9. Apparatus a's'defined in claim 6 wherein said intermediate portionisa rectangular-to-circular wave guide transition section.

' 10. An electromagnetic wave energy mode transformer comprising acontinuous length of hollow wave guide hav ing a central longitudinalaxis of propagation, a length of transmission line positioned within thewave guide along said axis, and energy pickup andradiating'meansterminating each end "ofthe transmission line whereby aportion of the energy transmitted along the wave guide is carried by thetransmission line, the length of the transmission line being such as toeffect a quadrature phase difference between the portion of energypropagated directly by the wave guide and the portion of energypropagated by the transmission line, the pickup and radiating means atone end of the transmission line being oriented at ninety degreesrelative to the pickup and radiating means at the other end of thetransmission line whereby the plane of the E-vectoi of the'energyradiated at one end of the transmission'line is rotated ninety degreeswith respect to the energy picked up at the other end of thetransmission line.

11. An electromagnetic wave energy mode transformer comprising acontinuous length of hollow wave guide having a central longitudinalaxis of propagation, a first portion of the wave guide being rectangularin cross-section and a second portion of the wave guide being circularin cross-section, a length of transmission line having the ends thereofpositioned respectively in the rectangular and circular portions of thewave guide, and energy pickup and radiating means terminating each endof the transmission line whereby a portion of the energy transmittedalong the wave guide is carried by the transmission line, the length ofthe transmission line being such as, to effect a quadrature phasedifierence between the portion of energy propagated directly by the waveguide and the portion of energy propagated by the transmission line, theenergy pickup and radiating means at one end of the transmission linebeing oriented at 90 degrees relative to the energy pickup and radiatingmeans at the other end of the transmission line whereby the plane of theE-vector of the energy radiated at one end of the transmission line isrotated 90 degrees with respect to the energy picked up at the other endof the transmission line.

References Cited in the file of this patent UNITED STATES PATENTS2,106,769 Southworth Feb. 1, 1938 2,129,669 Bowen Sept. 13, 19382,232,179 King Feb. 18, 1941 2,281,550 Barrow May 5, 1942 2,412,320Carter Dec. 10, 1946 2,425,345 Ring Aug. 12, 1947 2,441,598 RobertsonMay 18, 1948 2,443,612 Fox June 22, 1948 2,501,335 Hunter Mar. 21, 19502,545,472

Kline Mar. 20, 1951

